To keep articles in a sanitary condition, antimicrobial substances are applied to their surface under certain circumstances. For example, in food-handling facilities, domestic kitchens and medical facilities, it is required to keep the surface of the interior floor and walls, instruments, fixtures or other articles germ-free in order to prevent possible contact infection or poisoning caused by harmful microorganisms such as bacterial pathogens attached to their surface.
As means of conferring antimicrobial properties, methods have been known wherein a metal thin film is attached to the surface of the article. As antimicrobial metal thin films, paper and plastic films have been proposed that have a thin film of metal such as copper, silver or alloy thereof attached to their surface.
For example, Patent Literature 1 discloses a Sn—Cu alloy film containing a Sn—Cu alloy and 1 to 10 wt % of SnO2, as an antimicrobial metal thin film to be laid on a substrate. The literature discloses that the Sn—Cu alloy film is formed by forming a Sn layer and Cu layer by sputtering followed by an annealing treatment at high temperatures.
Studies been made to increase the wear resistance of metal thin films having antimicrobial properties. For example, Patent Literature 2 discloses a metal fibrous body containing fibers and metal coatings attached thereon, the surface of the coating exhibiting orange peel. The metal coating with orange peel surface is disclosed as having high adhesion strength and antimicrobial properties. In addition, Patent Literature 3 discloses an antimicrobial substrate having a base and a plurality of antimicrobial metal islands disposed on a surface of the base. The literature discloses that adjustment of contact angle of the antimicrobial metal islands can increase the wear resistance to maintain the antimicrobial properties for a long period of time.